Electrical intercommunication system



Sept. 8, 1953 J. J. B. LAIR ELECTRICAL.INTERCOMMUNICATION SYSTEM 6 Sheets-Sheet 1 Filed March 18, 1950 uaus/v a. B. LAIR AGENT Sept. 8, 1953 J. J. B. LAIR ELECTRICAL INTERCOMMUNICATION SYSTEM 6 Sheets-Sheet 2 Filed March 18, 1950 .1. J. B. LAlR 2,651,677 ELECTRICAL INTERCOMMUNICATION SYSTEM s Sheets-Sheet 5 Sept. 8, 1953 Filed March 18, 1950 INVENTOR JUL/EN a. a. LAN? BY AGENT Sept. 8, 1953 J. J. B. LAlR ELECTRICAL INTERCOMMUNICATION SYSTEM 6 Sheets-Sheet 4 Filed March 18, 1950 BY I M/ AGENT 3 Sept. 8, 1953 J. J. B. LAIR ELECTRICAL INTERCOMMUNICATION SYSTEM 6 Sheets-Sheet 5 Filed March 18, 1950 INVENTOR JULIE/Y d. B. LAIR AeNT Sept. 8, 1953 J. J. B. LAIR CTRICAL INTERCOMMUNICATION SYSTEM ELE 6 Sheets-Sheet 6 Filed March 18, 1950 mmunnqemmm a u v n a 010mm INVENTOR uuusn u. a, LA?

BY AGENT Patented Sept. 8, 1953 ELECTRICAL INTERCOMMUNICATION SYSTEM Jean J ulien Baptiste Lair, Nutley,

N. J assignor to International Standard Electric Corporation,

New York, N. Y., a corporation of Delaware Application March 18, 1950, Serial No. 150,437

9 Claims.

This invention relates to electrical switching systems and more particularly to switching systems of the kind employed in telecommunication, for example, in telephone, telegraph, etc., exchange systems.

The objects of the invention are to render the switching equipment less expensive to install and maintain in service than was heretofore practicable and to increase the speed at which desired interconnections are established.

The features of the invention and a detailed description of some preferred embodiments thereof will be described herein in connection with a telephone exchange system but it will be understood that the invention is not limited to telephone systems but is applicable to switching systems in general. Moreover, although a complete telephone switching system will be described as equipped according to the present invention some or all of the advantages of the invention can be derived from a partial application of one or more features herein disclosed and claimed combination with elements of other known or unknown switching systems.

Heretofore it has been useful to employ electromechanical or electronic switches for establishing connections, e. g. for the purpose of connecting a calling subscribers line with a wanted trunk. The switching devices employed at each connecting stage have comprised switches with movable wipers or have consisted of counting relays or a chain of electronic discharge tubes or the movable beam of a cathode ray tube or like device. This has been true with respect to the switching devices used to connect a predetermined or idle trunk with a calling one of a plurality of lines the so-called line finder operation, or to connect a predetermined calling line with a certain one or an idle one of a group of outgoing trunks the so-called line switching or trunk selecting operation, or to connect a trunk with a wanted subscribers line the so-called line selecting or connecting operation.

In accordance with the present invention any or all of the aforementioned switching operations are performed by static switching means or networks which effect the desired interconnections in a substantially instantaneous manner.

Considering first the so-called line switching or trunk selecting operation, there is provided in accordance with the invention, an electrical network the input of which may consist of a radio channel or transmission line. A plurality of calls, for example, calls originating at any one or more of s y 100 p ne su t t ons connected with said line are directed to the network in spaced time relation with respect to one another. For instance, reference pulses are cyclically and periodically impressed on the line and any call initiated at a station associated with the line is represented by a train of periodic station pulses each of which follows preceding reference pulse and is separated from it by a predetermined time interval characteristic of the calling station. Each station will thus be accorded a space time channel on the transmission line and may convey intelligence thereover by modulating its station pulses the repetition rate of which is, of course, above the audible range. It will be appreciated that the intelligence may be conveyed in any known form of modulation, such as space time modulation, pulse width modulation, amplitude modulation, etc.

The output of the network comprises a plurality of trunks, the number of trunks depending, as in electromechanical switching systems, upon the amount of traffic which the network is expected to carry. If, for example, it is desired to afford for each one of the sub-stations, in the case assumed above, simultaneous passage through the network to -an individual trunk, then the network will have to be provided with 100 trunks serving as outlets. In this case the station pulse of any given station, or say at station No. 59, will be directed to the trunk outlet 59, the station pulse of station No. '78 to outlet trunk '78, etc., etc. Thus the trunk outlets of the network will temporarily serve as individual lines for the stations connected in common with one and the same input line.

According to one of the features of the invention the network comprises an artificial transmission line, i. e., a so-called delay line of such effective electrical length that the incoming station pulses will be positioned, respectively, opposite their individual outlet trunks which are connected to the delay line at different spaced points along its length. The transmission of the station pulses which pass into the outlets is normally blocked by a uni-laterial contact device, such as a rectifier, or by a controllable high impedance device, such as a suitably biased gating tube. Each reference pulse, one of which occurs ahead of each block of station pulses, is employed for controlling means for momentarily unblocking transmission between the line and all of the outlet trunks so that the station pulses which previously appeared in timed succession on the input line will now appear simultaneously, that is, in time alignment with one another at the output trunks with each pulse now separated from the others in space, that is, in its appropriate outlet. Hereafter in this description pulses appearing on a single line or channel separated only in time will be referred to as in succession and those appearing simultaneously at the inputs of a number of trunks will be described as in alignment.

It is not essential to provide a separate trunk outlet for each station having access to the input line since, as is well known in electromechanical switching systems, such stations may be so equipped that more than a certain percentage of simultaneous calls is unlikely to arise at any particular time: thus, twenty or fewer outlet trunks may be allocated to serve a group of 100 potential calling stations.

Networks similar to those previously described may also be used in the reverse direction, that is to say, aligned pulses applied to the 100 trunk outlets may be caused to pass into the common transmission line in properly spaced time succession.

The applications of the invention so far described have been concerned with non-numerical switching operations, that is, with the routing of a call incoming over a common line to a trunk individual to it or temporarily reserved for it. When the invention is applied to numerical switching operations, the system must be provided with a means for producing a variable delay depending upon a dialed number or some other indication given by the calling station. The input side of such a system will consist of a plurality of incoming lines or trunks on which calls may arrive. For instance, the input side may consist of the 100 or fewer output trunks of the non-numerical connecting stage previously described. Pulses on an input line of this system or network are modulated over a predetermined period of time in accordance with a digit of the wanted partys number called by the calling station and depending upon this modulation the network will produce a predetermined delay. Assuming a decimal system of selection, from to delay units may be produced by the network to position the incoming pulses opposite to a called one of 10 outlet trunks. The passage to the called outlet is normally blocked and is opened only at predetermined intervals, that is, at the same frequency as the repetition rate of the reference pulses and since this is well above the range of speech frequencies, the transmission of intelligible speech or other signal intelligence may be effected without interference from any audible tone produced by the pulses.

The output trunks of a non-numerical switching stage need not be permanently connected to a common line over a delay line. They may instead, be successively connected to the common line through the medium of some form of distributor which may, for example, be of the cathode ray type.

The numerical switching stage may provide selection in accordance with more than one digit of the called number, for example, 10 delay units may be produced in the network in accordance with a dialed tens digit and a single delay unit may be produced in accordance with a dialed units digit, thus routing the call to a desired one of 100 numerical outlets of the connecting stage. Obviously, thousands and hundreds digits may be used in similar manner to route calls through a single network.

The above described interconnecting operations will now be described in greater detail with reference to the accompanying drawings in which:

Fig. 1 illustrates the instantaneous distribution on a portion of a common transmission line of one complete block of station pulses with respect to the reference pulses at each end of the group or block;

Fig. 2 illustrates the instantaneous distribution on a portion of a common line of a number of calling station pulses with respect to reference pulses for the purpose of showing a typical nor mal condition of the common line when several of the stations are making calls at the same time;

Fig. 3 is a diagrammatic representation illustrating a plurality of stations connected in parallel with a common line;

Fig. 3a is a transverse cross-section of a typical cable comprising a common line represented in Fig. 3;

Fig. 4 is a block diagram of an embodiment of the invention in a multi-stage telephone system;

Fig. 5 shows the time relationship between station pulses, station reference pulses, exchange reference pulses and network reference pulses in the system represented in Fig. 4;

Fig. 6 illustrates the time relationship of Fig. 5 when setting up a call from one exchange to another exchange;

Fig. 7 illustrates diagrammatically the establishment of both intra-exchange and interexchange connections;

Fig. 8 shows the circuit arrangement of a network arranged to align and distribute to individual lines station pulses which reach the network in succession over a common line;

Fig, 9 shows a network responsive to signalling pulses representing 2, called station to align and distribute to an appropriate individual outlet pulses which reach the network in succession;

Fig. 9a shows the operating characteristics of uni-lateral conducting devices such as rectifiers which are used in the network of Fig. 9,

Fig. 10 diagrammatically illustrates a modification of the network of Fig. 9 which is responsive to signalling pulses representing two different digits used in designating a wanted station, and

Fig. 11 shows a layout diagram referred to in the explanation of Fig. '7.

Referring now to Fig. 1, the reference pulses R recur at fixed intervals of time, for example, every 100 microseconds (ms) and between each two successive reference pulses, 100 relatively small amplitude pulses s may be produced each of which is characteristic in time position of a different sub-station and is identified in the drawings by the reference letter 8 followed by its sub-station number (e. g. s1, s2 $99). The width of each pulse s as illustrated in 0.49 ms. and the spacing between adjacent s pulses is 0.99 ms. The higher the number of the sub-station the further is each of its characteristic pulses separated in time from the preceding reference pulse R.

Fig. 2 illustrates for one type of system the transmission sequence of pulses when sub-stations S2, S6, S12 and S96 out of the 100 sub-stations connected with the common line have initiated calls at the same time. In. this type of system each sub-station generates its own s pulses appropriately delayed with respect to the reference pulses R. However, both the s and R pulses may, if desired, be generated at the central network, the s pulses being continually present in the common line at very low levels but the amplitude of thels pulses characteristic .of a partion is represented by a slight time displacement of the s pulses from their normal time vpos'itions.

As will be seen from Fig. 2, the spacing of substation pulse 82 from the preceding reference pulse JR is 2.97 ms., that of sub-station 86, 6,93 ms., and that of sub-station s12 1287 ms.

Fig. 3 illustrates diagrammatically a netwotk comprising multiple substations S0, S1, S2, Sc (599 connected in parallel with a-common cablecomprising lines ml, 102 and'l'l'l3. Thereference pulses R which control the timing of the s pulses of a group or 100 substations are sent from the central office over the .line lfll. Between the central ofiice and in series with line ml there is interposed a delay network L designed to delay the reference pulsesibyan amount equal to the diiierence between the predetermined time interval by which the so pulses are to follow the reference pulses Rand the time re quired for the transmission of an R pulse to station So from the central office over line [ill and for the transmission of an s pulse back to the central omce from the station So over time H12. Thus reference pulses which are supplied at the central exchangeand so substations pulses reaching the exchange over .line .152 will be properly separated in time. vA similar delay network L1 is interposed in ser'es withJ-ine It! .between the points thereof .at which substations So and S1 are respectively connected to \line Hill. This delay networklu delays the reference pulses by an additional-time interval which is equal to the diiTerence between the time interval by .which the 81 pulses are to follow the reference pulses and the delay resulting from cable .losses. .Other delay networks L2 L99 are similarly connected in series lalongline I172 'betweenits points of connection to successive parts of adjacent stations. In each substation there will be provided an 8 pulse generator which-is adapted to be triggered by the Rpulses at the instants when they reach the generator. Thus, each station produces its own 8 pulses at .100 ms. intervals properly retarded in time with respect to the reference pulses.

The s pulses may be sent ifromvanysubstation over line m2 towards the central oince or .exchange, voice modulated at that stationin any known manner, and the substations are able to receive over line 1G3, s pulses "which have "been modulated at anyother substation.

As illustrated in Fig. 3A, the lines l-Ol, tfiiand 193 in practice each comprise coaxial cables or shielded pairs enclosed within a common sheath 3?.

Fig. 4 shows in block -.diagrammatic form the method of connecting a calling substation tassociated with an exchange A with a :called substation associated wit; can exchange 123. There are indicated five lines ITBZA, associated respectively with five groups .of substations belonging to the exchange A, and .one line 1033 associated with one group of substations belonging .to exchange 'B. These all comprise that is, lines over which groups of 's pulses are common lines;

transmitted simultaneously, each s .pulse "having it characteristic time position with reference to the R pulses, as explained above. They correspond to thelike-num'bered lines shown in ,Fig. 3. "Each line 102A terminates at the exchange Ain an aligning network ll IDA, the function of which to align the impulses arriving from the calling substations. The construction of an aligning :netWOIkiS illustrated in greater detail in Fig. 8. 'The aligned impulses are transmitted to a switching position l'lilA.

"The first three digits of the called number sent :by .a calling station ,produce a delay in the s pulses of arca'lling substation on line IUZA which causes the call to be automatically routed towards the called exchange B. As indicated in Fig. -.4, the networks 11 0A and the switching position 513A are connected to a synchronising means 2A in order 'to maintain the relative positions of the pulses within the exchange A.

ll'irom the switching position H IA the calling pulses are directed over a cable USA or other transmission medium to an aligning network IMB at the called exchange B. The pulses received by the aligning network IMB are aligned with respect to the reference pulses of the exc'hangeiB and transmitted over separate circuits H513 to a receiving switchingposition HEB. To do this the reference pulse RNI of the network to which the station belongs is inserted .periodically between two of the incoming pulses at the input of the aligning network IMB, a for instance, by the synchronizing means 119B.

The thousands and hundreds digits dialed by the calling station will produce a delay causing the automatic routing of the call in thesame manner as at the transmitting switching positicn I l IA. The pulses are directed towards aligning receiving mean II'IB which aligns the pulses received with the reference pulses of the called cable IBSB.

"The tens and units digits of the called number produce a predetermined delay to align pulses with'the pulse representing the-called station.

At the called exchange B the networks [MB and the receiving switching position 6B are connected to a common synchronising means HQB which insures that the pulses of the called station reach the calling station ,via the transmission circuits of exchange B and the receivin circuits of exchange A.

IF-lg. 4 illustrates only the transmitting portion of the exchange A and the receiving portion of exchange B, but it should be understood that both exchanges are provided with receiving, as well as transmittingsides, as indicated in'Fig. '7.

In order to render the preceding description clearer, the relative positions of the'pulses in the different parts of the connection will now be explained with reference toFig.- 5.

The pulse 210 appearing on the top lines (4) represents a station pulse of substation cm which isassumed to helconnected to a cable No. 40 the characteristic reference pulse .of which is .indicated at RS411. The pulse 810 will be 10.89 ms. from the preceding reference puls R840.

The cable No. 410 is connected with a central exchange No. .20 which might, for example, be the exchange A and which .is identified byareference pulse REM, produced in the switching circuit llIA. Since the subscribers cable No. 40 is the fortieth which leads to exchange .No. 20, the reference pulse R840 is spaced (as indicated in line "3 for Fig. '5) 39.6 ms. from the exchange reference pulse REM. The reference 7 pulses RSI to RS353 of the other cables will be between the preceding exchange reference pulse REZB and reference pulse RS40, and the reference pulses R841, RS42, etc., of other cables will have a time position between RS4!) and the succeeding exchange reference pulse REZB.

Similarly, the exchange reference pulse REZU' (line 2, Fig. identifying exchange 20, is spaced 19.8 ms. from the reference pulse RNi (line I, Fig. 5) identifying the exchange network or system to which the exchange 20 belongs. The other exchange reference pulses RE will be to th left and right of exchange reference pulse RE20. The subscribers cable reference pulse RS4!) is spaced 59.4 ms. from the network reference pulse RNI.

Thus it will be seen that the same relationship exists between the reference pulses identifying the exchange and those identifying an exchange belonging to the network as between an exchange and its subscribers cables or sub-divisions. One switching stage is keyed to other switching stages by means of the time position of the reference pulses of the switching stages. The total number of such switching stages depends, of course, on the size of the exchange but the operations to be performed are of the same general nature in all the switching stages.

Line I of Fig. 6 shows a reference pulse RS43 of the calling subscribers cable and ten sub-- station pulses. Line 2 shows the reference pulses REX representing the exchange in which the cable terminates and the time displacement between REX and R48 may be represented by 152.

The system or network to which the exchange: X belongs is represented by the reference pulses RN! which are spaced 100 ms. apart, as indicated on line 3 of Fig. 6. The time displacement of reference pulses REX with respect to pulses RNi is represented by tl. The signals or series of pulses indicated on line I is, therefore, spaced from the network reference pulse RN! by distances of tl+t2 or t3. Thus the pulses produced in the calling substation line (line i of Fig. 6) must be delayed t3=100 t l +152) The sequence of pulses received from the calling substation lines will, therefore, be spaced from the reference pulse RN! of the network in the same manner as from the reference pulses RS 58 of the incoming cable. This is shown on line (4) of Fig. 6.

An aligning network separates the impulses received from the calling cable and places the pulses received from each substation on a separate circuit.

Referring now to Fig. 7, the pulses 818, 512, sa representing the three calling stations S2, S12 and SIB on cable No. 40, as well as the reference pulses RS 30 of the cable, arrive over line IBZA at the aligning network HOA of exchange A. The network IHJA will align these pulses so that each will emerge therefrom at the time of reference pulse R840 on a separate circuit as shown at 21, I21, and 81, connected to a transmitting switching circuit HIA.

Depending on the first digit or digits of the called number dialed to the switching circuit I i IA, the pulses I22 of substation 12 will be routed as described later towards a receiving alignment network 4A of exchange A, and the pulses 22 and I82 towards receiving alignment network I MB of exchange B.

The pulses 22 and I82 can be present at different times on the same line extending from IHA to 4B because they come from difierent switching circuits such as Fig. 9. Their time position is different because each circuit such as Fig. 9 has its characteristic timing which may be obtained for example as will now be described with :reference to Fig. 11. In this diagram switching networks M and N are similar to Figure 9. Since the called numbers (from M and N) correspond "to the same exchange B the outputs of the two :networks will correspond respectively to the lines ;230Lsivr and 230L5N. The two pulses 22 and 82 have to be transmitted to the exchange B by the same line 232115 which can carry one hundred pulses provided that they have different timing. Then if we assume that the pulses 22 and E82 and also all the other pulses coming from all the networks (similar to Figure 9) have the same timing when the exchange B is called it is possible to give at each network such as M, N, O, P etc. a specific delay different for each network. In that condition a multiplicity of pulses can be present in the same period of time on the cable 232L5 between exchanges A and B. The maximum number of pulses is limited by the width of the pulses corresponding to each channel. In the chosen example this number of pulses is one hundred at the maximum. The crystal rectifiers CM and Cu which conduct in the direction of the arrows permit the pulses coming from networks M and N to pass to the common line 232115 and prevent any pulse present (at different time) on the line 232L5 from passing back into the networks such as M, N, O, P etc.

It will be clear also that other arrangements can be utilized, for example, by grouping at the input of the network M all the circuits corresponding to a given characteristic timing, and at the input of the network N all the circuits corresponding to another characteristic timing, and so on for the other networks such as O, P, Q etc. This arrangement avoids the use of additional delay lines (such as shown in Fig. 11) and permits the use of the normal delay existing at the output of each cable.

At exchange B the output of alignment circuit IMB will align the pulses 22 and its in separate trunks leading towards the receiving switching circuit HEB from which responsive to the thousands and hundreds digits of the called number the pulses are sent in succession into an aligning circuit 1B and thence over the switching circuit 8B, which is responsive to the tens and units digits, to the receiving circuits of the called cable I033 of exchange B where the pulses 24 and 184 occupy the same positions with respect to the reference pulse RS4!) as the called stations occupy on the line with respect to the reference pulse of the receiving line [0318.

The transmitting branch 10213 of this cable is shown as carrying a pulse representing station 5 and a reference pulse RS1. Assuming that the called station is on cable No. 40 at exchange A, these pulses are received and the station pulses aligned in network HOB routed to the called exchange A over the transmitting switching circuit IHB' of exchange B to the receiving alignment circuit 4A of exchange A. In the output of AA pulse 53 will be aligned with pulse 23 which originated On line 102A and routed over receiving switching circuit IIBA, alignment network iilA, and switching circuit 8A. The pulses 124 and 54 will be directed over the receiving branch "13A of the called cable No. 40, so spaced with respect to reference pulse RS4!) that 9 they will reach, respectively, only substations and 12 connected with this cable. I

Fig. 8 illustrates the detailsfof the aligning circuits indicated by'the'blocks III IA', II4A, I'I'IA, IIIJB, H43, H13 of Figs. 4'and7.

At the left hand' side of the figure are i icated the two conductors o'f,- say', the line IIIZA over which a sequence or block comprising a maximum of 100 s-pul ses may be sent to the exchange from a group of one hundred substations.

The line I02A leads to a delay network IZII for adjusting the time of arrivalof these pulses at the central exchange and thence to an amplifier l2I. The relative I I I v I work I20 and the amplifier I2'I are immaterial and in some cases one may dispensewith an amplifier altogether. In any event the delaynetwork and the amplifier may be of suitable known construction.

The output of the amplifier I2I is fed into a delay line I22 to the duration of the pulse sequence, which in the present case consists of a-reference' pulse RS followed by a maximum of 100 station pulses ell-s99. These pulses willbe" distributed along the delay network H280 that when areference pulse RS reaches .a rectifier I'23R- the" station pulse 86 will be aligned with'an output branch I fillLil of the network I22 which contains rectifier I23s0, the pulse-sl' will be aligned with the branch I 30LI containing rectifier I 238i, etc. and the pulse s99 will be a ligned with the branch IEQLQQ of the network l22-which contains" the rectifier I23s99.

The amplitude of reference pulses' RS is larger than that of the station pulsess, and the reference pulses will be clipped along the dotted line indicated at I24 (Fig; 8)- by" the detector 123R which is so polarized or biasedbybattery I25 that only the portion of pulse RS'above-line 12s will be fed to an amplifier I26. I

Normally the detectors l23sfl l23s99 are so polarized by a battery I 21 that they block the passage of the pulses-s. When-however; the output of amplifier I26 is fed to circuit =I28 *then' for a brief periodof time determined by the width of the reference pulse RS,- the' rectifiers' I23sIl-99 will be unblocked and p'erm'it the stored impulses S0 to S99 to change the voltage impressed on impedances I29s0 -I29s99. Each of these impedances terminates a different output branch line I30L0, I30L'I", I30L2 I30L3, etc;, I3iiL99, producing in each line I30L apulsecorresponding to one of the pulses s sent-over cir-' cuit IOZA. The substation pulses'will'thus be aligned in the lines I30L' whereby the network, shown in Fig. 8 and corresponding to, say, IIIIA of Fig. 7, affords a temporary individual line I30L for each one ofthe substations S of Fig. 3. Of course, there will be pulses only on' these lines I3IiL which correspond to" calling substations S, in the case assumed in" Fig. 7 on lines I30L2', I3IILI2 and I30LI8.

Similarly, when 'the'n'etwork of Fig. 8is'used at any other point, say at I MA orfII 1A; it'will provide a separate individual output channel ISGL for each sequential"pulsethat'may reach it over a common channel. I

It will be obvious to those skilled'in' th'e'art that an electro-magneticor electronic distributor or finder switch may be-provided atthe input of the delay network of Fig.- 8 to insure moreeffective utilization thereof'than is'the case when the network is permanently cOnnected to-the positions of the delay netwhose electrical lengthis' equal such as IIIA.

10 cable serving substations. Such distributors are well known a'nd'on'e embodiment is shown in Fig. 9 in association with a switching position ation of a call on line X3is in'dicate'd'by the production of 10,000 pulses per second thereon. Depending on the position of wiper I40, and thus at the latest within of a second after the call appears on line X3, the line pulses will reach line I43 connected with the wiper I40, and als'c over rectifier CI'4I, through sensitive relay I4I, which becomes energized and stops the wiper I as on'th'e terminal I42of lin'e X3 in a manner well known in the machine switching art. Relay I II closes a circuit from battery over the holding windings of relays I45fI-f4. These relays are of the type which responsive to energization" of their holding windings only will not attract their armatures but after the energization of their right hand actuating windings, completion of their holding circuits will maintain their armatures attracted even after deenergization of the actuating windings.

Each substation is'provided with known means for producing currents of four different frequencies which may be combined into a code of ten numbers. Preferably these four frequencies are within one octave, whereby the second harmonic of any of these frequencies cannot fall within the range of the calling number frequency band. The centers of adjacent frequencies may, therefore, be sufficiently spaced to avoid confusion and these frequencies should preferably be outside of the range of the audible frequencies. They may, for instance, be between 100 and 200'cycles, e. g. fl 100 cycles, )2 122 cycles, f3 148' cycles and 14 cycles. The ten possible combinations of these frequencies may be #1=fI, #2:]2, #3=fl+f2, #4:]3, #5=fl+f3, #6=f2-{ -'f3, #7:)4, #8= I+f4, #9=f2+f4', and 0=f3+f4.

A group of four filters'FI-F4 is normally connected over an amplifier M l'and decouplin resistors RI-R4 to the line I43 over contacts of a relay I45. of any known construction, each tuned to a different one of said frequencies fI-J4. Relays I45fl, I45J2, I45f3, I45f i" are, respectively, connected to the outputs of the filters Fl-F lover' pulses to an extent determined by the called number, and thus delay networks lee may produce a code corresponding to ten difierent numbers. A delay will" be produced when all the four relays I45fI- i remain de-energized; oneunit of delay is produced by network I45JI when- These filters are band pass filters only relay I451! is energized; two units of delay are produced by network l46f2 when only relay l45f2 is energized; four units or delay are introduced by network I48f3 when only relay 14513 is energized; and seven units of delay are introduced by network Mfifl when only relay |45j4 is energized.

The unit of delay may be of any suitable value, e. g. between one-half and ten microseconds, but sinc it is correlated with the timing of the pulses in the other circuits it is made equal to .98 microsecond, i. e. to the time afiorded for each station by the spacing between two station pulses s. The ten units of delay may be introduced in the circuit illustrated in Fig. 9 so as to produce the following results when a digit from 1 to is dialed:

Dial 1-frequency f1; relay [45h energized; delay network |45f1 cut in; one unit of delay.

Dial 2frequency f2; relay l4'5fz energized; network Mfifz cut in; 2 units of delay.

Dial I i-frequencies f1 and f2; relays 14533 and "Biz energized; networks M-Bih and Mfifz cut in; 3 units of delay.

Dial 4-frequency f3; relay l45f3 energized; network [481% cut in; 4 units of delay.

Dial 5--frequencies f1 and f3; relays 14511 and [45 3 energized; networks l46f1 and l iiifz cut in; 5 units of delay.

Dial 6-frequencies f2 and f3; relays M573 and |45f3 energized; network I46 and "W3 cut in; 6 units of delay.

Dial '7--frequency f4; relay M512 energized; network 146i. cut in; '7 units of delay.

Dial 8frequencies f1 and f4; relays [45h and Sir energized; networks 145]1 and [45,121 out in; 8 units of delay.

Dial 9-frequencies f2. and f4; relays lfifz and l45f4 energized; networks [46b and H612 cut in; 9 units of delay.

Dial l0-frequencies f3 and f4; relays l ifs and [45 4 energized; short circuiting networks I461; and "W4; 0 units of delay.

Whenever a relay MSJl-A is energized over its right-hand actuating winding it holds over its holding winding after deenergization of its actuating winding. Relay I48 also becomes energized and over its upper contacts extends the dialling circuit to the next selecting stage, and relay 145 also becomes energized, whereby the next digit is prevented from reaching the filters FI-F4.

When a subscriber hangs up or some other indication is given that line X3 is no longer in a calling condition, the relay l4! immediately becomes de-energized allowing th distributor brush M0 to continue its rotation. Deenergization of relay Ml causes the release of relays I45, I48 and M8.

At the time that the call on line X3 stops the distributor MB on the No. 3 terminal M2, the circuits of relays I45h-l45f4 are closed, whereas the circuit of relay I48 is open. For instance, the dialing of digit 5 sends over line I43 frequencies f1 and f3, whereby through the agency of two of the filters Fl and F3, relays M5 and 145 3 are energized and relay I48 is energized, which introduce by means of networks 146;1 and 146 five units of delay in the line M? as compared to the line M3.

The pulses sent over line X3 and selectively delayed by networks M61! and l46f3 will, therefore, be sent into the delay line 228 whose total length corresponds to ten of said units of delay. Ten equally spaced lines 230L0, 230Ll, 23012 12 230L9 are uniformly branched off the delay network 228, each containing a detector 22350 223s9. A battery 221 so polarizes these detectors that they will normally ofier infinite impedance to the passageof pulses from network 223. An auxiliary pulse generator 23! connected with the network applies unblocking pulses over a ten unit delay line 232 to the terminals of a relatively small resistance 233.

Lets us assume that the magnitude of this pulse is at least equal to V1 and that the ampere-volt characteristics of the detectors 223 are as represented in Fig. 9A in which V2 is the amplitude of each positive pulse received on the network 228 and the resultant amplitude V1EVz produces no current in the rectifier. While the pulse V1 persists, the detector 223 will be polarized at least to the potential V0 or more. At this instant the pulse having no delay will be at detector 223s!) and the pulse having five units of delay will be at detector 223s5.

The ten detectors 223 to which V0 polarizing voltage is applied under the control of the unblocking pulses received from generator 23L permit the passage of pulses having an amplitude of V2 (Fig. 9A). The impulse representing digit 5 will therefore reach line 230L5 at the same time as impulse which has 0 units of delay reaches the line 230m. However all the pulses which reach the lines 236L will have the assumed delay of ten units with respect to the reference pulse of the network which, through the agency of 23 I, controls the alignment just described. Since this reference pulse is a constantly recurring pulse, it may be given a sufilcient advance so that once the called exchange is reached the reference pulse will be aligned therewith.

If, for instance, three digits must be dialed to reach the called exchange, then all calls must pass through three circuits like the one shown in Fig. 9, and will reach the called exchange with a delay of thirty units, or 29.4 microseconds.

Again referring to Fig. 8, it is noted that the detector 123R and amplifier 126 are within a dotted square l3l to indicate that they may be replaced by an impulse generator synchronized to the reference pulse of the central exchangeto which they belong and which corresponds to. the generator 231 of Fig. 9.

It will be obvious to those skilled in the art the unidirectional devices or detectors indicated in these figures may be of any suitable type, e. g., dry rectifiers or vacuum tubes. For instance, an amplifying pentode may be used whose control grid is connected to the delay line and the cathode to the common return path. Such a pentodemay be blocked by the absence of plate potential and may be unblocked by an impulse applied to the plate. The blocking of such a tube may be afiected by the biasing of its cathode or grid or control grid or suppressor grid. The unblocking may be effected by applying a pulse of suitable amplitude and direction at the desired time.

According to another modification the calling lines may delay the pulses to such an extent that two or three successive digits of the called number will be indicated. Such an arrangement responsive to two digits is shown in Fig. 10.

All elements in Fig. 10 which bear the same reference numerals as in Fig. 9 perform the same functions. The first delay line comprises in addition to the delay networks I46f1, Mfifz, MBjs and Miiii and the associated control relays l45 1-i45f4, four additional delay networks Biro, 146m, MB ao, andllfifio arranged to introduce a delay ten times as great as the delay introduced by I46fr-l46f4. Relays l45f1o, [45]20, 145m and l45f4o are associated with these additional delay networks and are provided with contacts to cut them in and out of the circuit in the same manner as relays l45f1-l 45]4 control the first group of delay networks.

The first delay line may be associated over a line [41a with the second delay line 228a under the control of relay I48. Line 228 of Fig. 9 has an electrical length equal to ten units of delay and could accommodate only ten lines 2301.0 to 230L9. Line 228a has a length equal to one hundred units of delay and accommodates one hundred lines 230aLo230aL99. An impulse generator 235a sends into line 228a pulses spaced by one hundred units of delay. If the unit of delay is equal to the time generally reserved for each substation, then the generator 2am may be dispensed with and the reference pulse of the exchange may be applied to the, line 22811 as in Fig. 8.

The operation of Fig. 10 is as follows:

When a call is initiated on one of the lines Xo-X4, the brush hill will stop on the terminal Hi2 of the calling line, relay I45 becomes energized, as does relay [4! to top the finder me. The circuits of relays I 45]1-74 and l45f1o- 4o are closed. The relay M8 is deenergized. The relay M8 is in a position in which its four armatures iefifi, 150;2, lfiiifs, and 156]4, connect the four filters of 46 with relays 1 4513-12, respectively. The first digit over the calling line will, therefore, operate one or more of these four relays as in the circuit of Fig. 9 and the instant this happens the relay M8 is energized and moves its armatures I55 into engagement with the lower set of terminals to disconnect the filters I44 from relays |45fl-f4 and connect them to the windings of relays l45f10-f40. Relay Hi5 remains energized. The next digit dialed over the calling-line will operate one of the relays '45f10-f40 in order to introduce into the line I43 an additional delay which is ten times as great as the delay introduced when the preceding digit was dialed. The nergization of any one of the relays I45fm-l45f4o will cause the deenergization of relays I48 and I45 as in Fig. 9.

The impulse sent out over line Mla will have a delay of -9 delay units produced by the insertion of networks MSfi-Mfijl in certain combinaions, and an additional delay of 0-90 units introduced by a suitable combination of networks l lfifm-l ltfiu. If, for instance, first thedigit and then the digit 9 were dialed, then a total delay of 95 units will be produced, and the delay line 228a will receive the unblocking signal when the pulse arriving over line ld'la is opposite outgoing line 23liaL95. The pulses appearing on the outgoing lines will all be aligned.

Obviously, delay networks may be provided in the system illustrated in Fig. 10 which would introduce delays of hundreds or units. This would require a much longer delay line 228a and the sending by generator 231a of an unblocking impulse for every ten normal pulses, introducing a transmission delay of one thousand microseconds.

What I claim is:

1. In a communication system a plurality of transmitting networks from which a plurality of separate signals are to be transmitted, a plurality of receiving networks each adapted to receive a plurality of separate signals, a plurality of selecting networks, each of said transmitting networks being connected to a receiving network by a single transmitting medium, each of said transmitting networks comprising means for producing a plurality of repetitive pulses on the associated transmitting medium at the same rate of repetition and spaced from each other in time, there being one pulse for each signal to be transmitted, means for modulating said pulses respectively with said signals, and means for producing a reference pulse at the same repetition rate as said signal pulse which has a different time position from reference pulses of other transmitter networks and provides an identification for said transmitting network, each of said receiving networks comprising a delay line, a plurality of output lines connected at spaced points along said delay line, there being one output line for each signal to be received and the delay between any two adjacent points being equal to the time displacement of the respective corresponding pulses, means for normally blocking said output lines, and means responsive to the receipt of a reference pulse for simultaneously unblocking said output lines at a time when said signal pulses are at respective points in said delay line at which said output lines are connected, whereby one signal pulse is applied to each output line, each of said selecting networks comprising means for connecting said network to any output line of a receiving network, a delay line, a plurality of output circuits connected at spaced points to said delay line and representing directions to be selected, means connected between said connecting means and said delay line and responsive to directive signals appearing as modulation of a re-' ceived signal pulse for delaying said received signal pulse for a time period corresponding to the desired direction to b selected and equal to the delay of the point on said delay line corresponding to said direction, means for normally blocking said output circuits, means for producing an auxiliary pulse having the same repetition rate as said signal pulses and at a time different from the times of auxiliary pulses of other selecting networks serving the same directions, and means for utilizing said auxiliary pulse for simultaneous- 1y unblocking said output circuits at times corresponding to the times that a delay pulse will pass an output circuit, whereby a delay pulse passing through said delay line will be applied to the desired output circuit.

2-. In a communication system, the combination, as defined in claim 1, in which the means for normally blocking the output lines of a receiving network comprises a rectifier in each out-- put line, means for normally biassing said rectifiers so that the pulse can not. pass therethrough, and the means for unblocking said-output lines comprises means responsive to the received refer-- ence pulse to alter the .bias on said rectifiers to permit the time spaced pulses in said delay line to pass simultaneously on to said output lines.

3. In a communication system, the combination, as defined in claim 2, in which the means for normally blocking the output circuits of a selecting network comprises a rectifier in each output circuit and means for normally ibiassing said rectifiers so that the pulse can not pass therethrough, and the means for unblocking said output circuits comprises means for producing a recurring auxiliary pulse at the repetition rate of the received pulse, and means for utilizing said auxiliary pulse for altering said bias to permit the passage of a pulse through said rectifiers at the time of said auxiliary pulse.

4. In a communication system, the combination, as defined in claim 1, in which the means 15 for normally blocking the output circuits of a selecting network comprises a rectifier in each of said circuits and means for normally biassing said rectifiers to prevent the transfer of pulses therethrough and the means for unblocking said output circuits comprises means for producing a recurring auxiliary pulse at the repetition rate of the received pulse, and means for utilizing said auxiliary pulse for altering said bias to permit the transfer of a pulse through said rectifiers at the time of said auxiliary pulse.

5. In a communication system, a plurality of transmitting stations divided into groups, a plurality of selecting stages, single transmission media for respectively connecting groups of stations with selecting stages, means for producing a recurring reference pulse on each transmitting medium, said pulse being spaced in time from the pulses on the other transmitting media, means for transmitting signals from the calling station of each group as modulated pulses on the associated transmitting medium, respectively spaced in time from said reference pulses, aligning means at each selecting stage comprising a delay line and a plurality of output lines connected at spaced points to said delay line, there being one output line for each signal to be received and the delay between any two adjacent points being equal to the time displacement of the respective coresponding pulses, means for normally blocking the flow of pulses from said delay line to said lines, means responsive to a received reference pulse for unblocking said lines to permit pulses in said delay line to pass simultaneously on to said output lines, selecting means at each selecting stage adapted to be connected to one of said output lines and including a delay line, a plurality of output circuits connected at spaced points to said delay line, and means responsive to signals representing a direction and appearing as a modulation on a pulse passing through said selecting means for delaying said pulse by a time period corresponding to the desired direction and equal to the delay of the point on said delay line corresponding to said direction, means normally blocking said output circuits, and means for unblocking said output circuits at predetermined recurring times corresponding to the times when a delayed pulse is passing an output circuit, whereby a puls delayed by said delaying means will be applied to a particular output circuit.

6. In a communication system, the combination, as defined in claim 5, in which the means for normally blocking the flow of pulses from the first mentioned delay line to the output line comprises a rectifier in each output line and means for normally biassing said rectifiers so that the pulses 16 can not pass therethrough, and the means for unblocking said lines comprises means responsive to the received reference pulse to alter the bias on said rectifiers to permit the time spaced pulses in said delay line to pass simultaneously on to said output lines.

'7. In a communication system, the combination, as defined in claim 6, in which the means normally blocking the output circuits of a selecting network comprises a rectifier in each output circuit and means for normally biassing said rectifier so that the pulse can not pass therethrough, and the means for unblocking said output circuits comprises means for producing a recurring auxiliary pulse at the repetitive rate of the received pulse, and means for utilizing said auxiliary pulse for altering said bias to permit the passage of a pulse through said rectifier at the time of said auxiliary pulse.

8. In a communication system, the combination, as defined in claim 5, in which the means for normally blocking the output circuits comprises a rectifier in each of said circuits and means for normally biassing said rectifiers to prevent the transfer of pulses therethrough, and the means for unblocking said circuits comprises means for producing a recurring auxiliary pulse at the repetitive rate of the received pulse, and means for utilizing said auxiliary pulse for altering said bias to permit the transfer of a pulse through said rectifier at the time of said auxiliary pu se.

9. In a communication system, the combination, according to claim 5, further comprising means for applying other pulses to said output circuits produced at different times from the outgoing circuits of other selecting stages, said pulses being spaced in time, and means for applying a reference pulse to each output circuit to form a train of signal pulses including a reference pulse.

JEAN JULIEN BAPTISTE LAIR.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,172,354 Blumlein Sept. 12, 1939 2,262,838 Deloraine et al. Nov. 18, 1941 2,416,330 Labin et a1. Feb. 25, 1947 2,418,116 Grieg Apr. 1, 1947 2,449,819 Purington Sept. 21, 1948 2,471,253 Toulon May 24, 1949 2,492,344 Adams et a1 Dec. 27, 1949 2,508,602 Peterson May 23, 1950 2,513,335 Labin et al. July 4, 1950 2,541,076 Labin et a1 Feb. 13, 1951 2,567,203 Golay Sept. 11, 1951 

